This invention pertains to the art of current sensing and more particularly to a remote non-invasive current sensor which senses current in a conductor located on a surface or below the surface of an object under test.
The invention is particularly applicable to the measurement of current in devices implanted within a human body, such as pacemakers. A further application is in non-biological settings including the servicing of electrical/electronic devices, testing of electronic circuit boards, and in the manufacturing of electrical/electronic equipment. It will be appreciated, however, that the invention has broader applications and may be advantageously employed in other embodiments and applications where access to current carrying conductors is difficult.
The measurement of current is necessary in many situations including development, testing, maintenance, and servicing of electrical/electronic devices. One such implementation is found in the medical field where it is desired to measure the current within a device implanted in a patient. Another area of use is in the measurement of current on a circuit board of an electrical/electronic device. The current carrying conductor in these situations may be either attached to a surface, or imbedded within the object under test. In either situation, sensing current is difficult, due to the location of the conductor.
Presently, there are two common current measurement techniques. The first technique involves physically cutting the conductor to allow insertion of a current measuring device. This technique cannot be used in many settings such as when the conductor is in a pacemaker implanted in a patient or when the conductor is attached to a circuit board.
Another current sensing technique involves surrounding the conductor in a coil, such as toroid coils, or other element which acts to concentrate electromagnetic waves. When toroid coils are used, the sensors are made to vary in direct proportion to the magnetic field to thereby obtain a current output.
Other current sensing devices which surround the conductor employ magneto-resistive elements such as those described in Baran, et al. U.S. Pat. No. 4,857,837. This patent teaches a current sensor with a magneto-resistive sensor having high fidelity of output. This current sensor is described as including a magnetic flux concentrator substantially encircling the electrical conductor. A patent to Milkovic U.S. Pat. No. 4,414,510 discloses a sensing system and method employing an anisotropic magneto-resistive ferrite member. Disclosed is a sensor having anisotropic magneto-resistive properties, where the conductor is encircled by an insulating surface and a permanently magnetized ferromagnetic member.
Among the drawbacks in existing current sensing techniques is a requirement of either cutting the conductor carrying the current or requiring the conductor to be encircled/enclosed within the sensor element. These techniques do not teach an easy manner of measuring current in a conductor attached to a surface of or embedded within an object or in other hard to access locations.
Therefore, it has been deemed desirable to develop a current sensor device which does not require cutting a conductor to insert the sensor device or require encircling/enclosing the conductor within the sensor device. Further, the sensor device should be able to measure current in conductors located below a surface of an object, as well as current in conductors attached to the surface of an object. It is further desirable to provide for the localization of the wire carrying the measured current and to obtain miniaturization of the sensors.